There is known a metal foil resistor in which a resistance circuit pattern is formed in a metal foil attached to an insulating substrate with an adhesive, and this whole substrate is encapsulated with a resin coating. In this type of resistor, it is necessary to reduce a change of a resistance value with respect to a temperature change as much as possible, that is, reduce a temperature coefficient of resistance (hereinafter referred to as TCR).
An increase of the TCR is mainly due to the difference of the thermal expansion coefficient between the metal foil and the substrate to which the foil has been bonded or the difference of the thermal coefficient between the metal foil and an adhesive or cement for bonding the metal foil and the substrate. Due to the differential thermal expansion coefficients, a stress is applied to the metal foil by a change of an ambient temperature and self-heating of the metal foil resistor, and thereby the metal foil is strained or distorted. For example, a Ni-Cr metal foil and a ceramic substrate differ significantly in the thermal expansion coefficient. Therefore, it has heretofore been known that the resistance change due to the temperature change of the metal foil itself is used for compensating the influence of the strain or stress induced by the temperature change on the TCR so as to reduce the TCR.
More specifically, the TCR is reduced by appropriately setting a material, a thickness, a thermal treatment and the resistance circuit pattern of the metal foil, materials and thicknesses of the substrate and the adhesive (cement) or the like. In Japanese Patent Publication (KOKAI) No. 2004-179639 (corresponding to U.S. Pat. No. 6,892,443 and EP 14227301A1), there are described examples of set numeric values of such design elements (control factors).